Agreed ... we all learn a lot from participating in this Forum. And the statement regards experience was not meant to be directed at you (or anyone else in particular) ... just an important consideration, that no-one ought to be "proclaiming" at us with fixed rules that are immutable for periodic verification.

The takeaway (for me) is that nothing much has reasonably changed ... some see it potentially dangerous, others not (depending) ... but it (the cpc) isn't as it should be regardless. There maybe a majority lean towards potentially dangerous.

In terms of an eicr regarding the question, would then a whole installation be unsatisfactory for continued use with the issue as described (and if that were the only matter)...I foresee in my crystal ball that a similar result of  opinion would be.

In the end much of anything can be made potentially dangerous can't it whether the starting point is ideal, or less than.

Peace and good health.

psychicwarrior said:

"How can there be a satisfactory Zs " - because there is at each accessory as each is still connected to one leg of the discontinuous CPC  ?

But only if thermal constrains are met.

There is a 'max Zs' for protection against electric shock, but also a 'max Zs' for protecting the cpc against thermal effects (at least with a fuse, or in the thermal region of a circuit-breaker).

In practice, with a 32 A BS 88-3 fuse, Za (loop impedance for thermal effects) is greater than Zs (loop impedance for ADS).

BUT - if a BS EN 60898 mcb is protecting the circuit, a B32 usually requires at least 2.5 sq mm cpc - but 1.5 sq mm might be OK for prospective fault current levels (at the origin) below 3 kA. So a 'complete ring' cpc might be necessary to meet the thermal constraints.

psychicwarrior said:

nothing much has reasonably changed

Agreed (from another perspective) ... a question is posed without all the necessary facts to make a decision, and then it's "no surprise" when "no conclusion is reached" (see my post a few mins ago regarding thermal constraints)

So I think the likelihood of a single CPC melting during a fault is low.

Actually meting the copper is highly unlikely - it would have to reach well over 1000ºC - but many problems can occur at much lower temperatures. A hot c.p.c. is likely to start melting insulation in its vicinity, even acting like a cheese wire cutting through the cable construction where there's any stress (e.g. at bends) or causing thermal damage to to internals of accessories - and not just at the point of the fault but all through the circuit upstream of the fault - with consequential dangers ranging from shock to fire.

So a 'complete ring' cpc might be necessary to meet the thermal constraints.

I'm not following the thinking here. Ring design normally only considers a single conductor as far as faults are concerned - as there's no guarantee that the fault current will divide significantly between the two legs - either because the fault is close to the origin of the circuit on one leg so the vast majority of the current passes along that leg - or because it's on a spur and there is only one conductor anyway. To my mind the comparison of measured Zs to acceptable values takes into account ADS, thermal withstand and differences in conductor temperature - e.g. in simple terms it satisfies the OSG Zs tables rather than just BS 7671 chapter 41 ones.

In a way, the increased Zs due to a broken c..p.c. in a ring is no more onerous than having a longer complete ring that measured the same at the end of a spur.

So say we'd identified the problem as G/Y sleeving having slipped into a terminal before it was tightened (and were under orders not to correct faults found) - and Zs at all points was satisfactory and no requirement to handle high protective conductor currents - certainly doesn't meet all BS 7671 requirements - but where is the danger (potential or otherwise) - that could occur from this situation that could justify a C2?

   - Andy.

psychicwarrior said:

let's say nominal 0.45 end to end L & N

Now we have a bit more information in this perhaps hypothetical situation!

I am struggling so far with the idea that a responsible electrician would just code, "C3" and move on to the next job.

A reasonable starting point would be to do the EFLI test on a sample of sockets i.a.w. Table 3.4 and Note 4 of GN3. If there isn't the expected gentle rise and fall of the values from the DB to the centre of the ring and back, test all of the sockets. Now we know that there is a break in the ring, but it could be line or cpc.

Our electrician has now found that line and neutral are intact, but IMHO we are still at the FI stage.

We know where the break is from the EFLI tests, so now the sockets need to be inspected. If the spiders have undone one of the terminals (or initial verification was incomplete), just put the conductor back, re-test, and no code at all. Everybody is happy for a few minutes' work.

If the terminals of both sockets are satisfactory, I think that the discontinuity of that particular segment of the ring needs to be confirmed.

Only now can we use some judgement and decide which code is appropriate and, depending upon the route of the defective cable, provide a quote for remedial work.

AJJewsbury said:

I'm not following the thinking here. Ring design normally only considers a single conductor as far as faults are concerned

Not quite true, because we use the ring-value of R2 to calculate anticipated Zs for circuit length, not the single-conductor value, i.e. we use [(R2/2)//(R2/2)] and not [R2/2]  ... although as I said in the earlier post, for 1.5 sq mm, in general Za > Zs (terms as defined in EIDG) and therefore shouldn't be an issue.

But it it's 1 sq mm, it won't meet the criteria  for breakers, regardless of whether Zs is met for ADS.

because we use the ring-value of R2 to calculate anticipated Zs for circuit length

True, in terms of circuit length, but in terms of maximum allowable Zs, considering ADS & thermal withstand, the assumption is that 100% of the fault current flows through a single conductor - so if max measured Zs is still within limits even with a break in the ring c.p.c. -  then things should still be OK both withstand & ADS wise. Had the circuit been longer, the break in the ring c.p.c. may well have pushed measured Zs above limits - but that not the situation the OP described.

Yes 1mm² c.p.c.s on a 32A OPD are going to be an issue - but that's the same whether the ring c.p.c. is intact or not (or for a spur).

   - Andy,

"hypothetical situation"

Nope , it is not !   there are plenty of discussions on the web - it's even been discussed here in the past.

To save providing every parameter of a scenario i had hoped the great and good folk reading to use some faith (but meh what's faith when it's about science they cry )  when reading the question and presume that the protective device was ok with the conductor size(s), Zs good at all points  and so on - all what one could quickly determine without a deep delve into what may or may not be underneath ...  the only issue apparently was that the  circuit was presenting a discontinuous cpc (seemingly at one point for some reason).

After that, then to ask if it was potentially dangerous situation (technically and/or in terms of an eicr  as later commented) or just a case of improve it at some point.    I was curious as there has been split opinion (majority perhaps leaning to potentially dangerous), so I thought I'd see whether that would be the case still.    

Walking away and leaving it as a responsible electrician  is not in the question to evaluate    by the way :-)

If it is an irritating question because of my original lack of details or in any case, I am sorry - it wasn't intended.

If I recall, some of Andy J comments below are not dissimilar to others I have read previously when this issue cropped up.

Good stuff.   Take it easy.

AJJewsbury said:

so if max measured Zs is still within limits even with a break in the ring c.p.c. -  then things should still be OK both withstand & ADS wise

Perhaps best to put this in the plainest terms possible (and in doing so, I fear this may not sit well given some of the previous posts ... apologies in advance if that's the case).

If there is a break in the cpc of an RFC, in BS 7671 terms (otherwise the installation didn't comply with with BS 7671 requirements for protective conductors of RFC, see 543.2.9) there is a fault in the circuit.

BS 7671 only concerns itself with single-fault conditions, and therefore I think weigh of argument is that it's not possible to use BS 7671 alone to justify a condition as being 'satisfactory' where a fault has already occurred.

This is where the individual inspector's faith in their own competence comes in, because they have to make a decision.

Based on the guidance (e.g. BPG4 as previously referenced), we might make the decision that, because there's already a single fault, requirements for  ADS and protective conductors are not met, so C2 is the minimum justifiable code.

On the other hand, we might ignore BS 7671, and choose to make an argument as to why we think it's safe ... but that's down to the person carrying out the periodic verification individually.

I think at this point, John Peckham  would be advising us that whatever we decide, we need to be sure that we can justify that when (to completely rip off John's turn of phrase)  'gripping the rail' ?